Recent optical communication system is implemented with an optical signal source including a semiconductor laser diode (hereafter denoted as LD) driven by a DC signal and an external modulator to modulate light with a continuous wave emitted from the LD to generate a modulated signal light. The external modulator may be a type of a Mach-Zender modulator, an electro-absorption (EA) modulator and so on. A United States patent published as US 2012/134620A has disclosed such an external modulator of the Mach-Zender type.
An optical transceiver applicable to the optical communication system generally includes an optical source, an optical modulator, and an optical receiver. The optical receiver receives an optical signal provided from an optical fiber coupled with the optical transceiver; while, the optical modulator modulates light of a continuous wave output from the optical source to provide modulated light into another optical fiber also coupled with the optical transceiver.
The optical modulator receives not only the continuous wave light from the optical source but electrical signals to modulate the continuous wave light. Moreover, an object to install the external modulator is to modulate the light with extremely high frequency signals, for instance, exceeding 10 GHz sometimes reaching 25 GHz. Such high frequency signals are easily to be degraded by interconnections. Accordingly, the optical modulator is necessary to be designed such that the optical arrangement is consistent with the electrical arrangement.